In Britain, the last occasion when nationalism of this sort prevented a foreign takeover came in the Thatcher era. The prime minister was determined to privatise ­British Leyland, the state-owned vehicle manufacturer, and a wonderful opportunity to do so emerged at the end of 1986. Two proposals were put to the government, one from Ford to buy British Leyland’s car business and the other from General Motors to buy Land Rover and trucks. When news of these proposals leaked out, there was an outburst of what Mrs Thatcher called “pseudo-patriotic hysteria” on the Tory back benches and in the Cabinet; both deals had to be abandoned. The prime minister was greatly irritated. As she wrote in her autobiography, “the idea that Ford was foreign and therefore bad was plainly absurd”.

A few years later what was left of British Leyland was sold to the German company BMW, and everyone heaved a big sigh of relief. By that time Thatcherite ideas on free markets had won the day, and the concept of national champions was largely dead. The British economy is stronger as a result.

Yet the protectionist tide is running strongly around the world, and there is a faint risk that, if other governments put up obstacles to takeovers by foreign companies, the British government will feel obliged to do the same. That temptation should be resisted.

There may be rare cases where a government needs to intervene for reasons of national security, but Britain gains far more than it loses from being an open economy. Foreign investment brings capital and management into the country, and puts competitive pressure on ­domestic firms.

The classical liberals argued in the 19th century that unilateral free trade was in Britain’s best interests, irrespective of what other countries did. The same is true of foreign investment.